I don't mean to be rude either, but I do happen to know what I am talking about.
Lobo dun is a term that is thrown around to refer to brown based dun in some areas. However, it's like me saying "taffy" instead of silver dapple. It's a regional term.
The horse attached does not have the dun gene at all. There is no dilution of the coat at all - the VERY FIRST thing a dun gene would do. Secondly, there are no dun factor markings. The photo gives a very clear view of the dorsal stripe you are talking about, and I can tell you right now, it is caused by countershading, and is often found in brown horses. A true dun has a clearly defined dorsal. There is none of the smuttiness the horse attached has. As for the lighter soft points (under the tail, on the flank, inside the elbow, around the muzzle, around the eye), these are caused by the brown colour. Brown horses are just like bay horses - they can and do have black points (legs, mane, tail etc). It is a form of the same gene that causes bay.
This is the brown horse I am talking about.
As for these horses, they are both grey. How you do not see that, I do not know. The difference in shade is because the horses are A - different ages, and B - different base coloured. The one on the right may well have been born dun - that is not going to stop her from going grey. Grey is a blanket - it covers the horse's original colour.